The invention relates to heated hair styling appliances. In particular, the invention pertains to a conductive heater and control for a curling iron which provides even heat distribution, temperature feedback, fast temperature recovery and various safety and convenience features.
Many conventional heaters for hair curling irons rely on radiation to carry energy to the barrel portion for heating the hair. Such radiative heaters are inefficient and are difficult to control by temperature feedback.
A heater as shown in U.S. Pat. No. 4,697,006 is coupled to the barrel for conductive heat transfer but requires a complex support to maintain the heater in contact with the barrel. The exemplary conductive heater also has by design an uneven or unbalanced heat distribution.
Conventional hairstyling appliances employ various methods and devices for regulating temperature including expensive negative temperature coefficient of resistance (NTC) or positive temperature coefficient of resistance (PTC) thermistors. These devices generally provide temperature control by changing the circuit resistance with increasing temperature within the barrel for example. In addition to the expense, some of these devices are cumbersome and are difficult to place within the barrel to obtain accurate temperature feedback.
In addition to the foregoing, hairstyling appliances employing inexpensive thin wire heater elements are not universally adapted for use with different voltage systems (e.g. 110 V in the United States versus 220 V in Europe). If not rewired, high voltage can cause the heater element to fail. Thus, a different heater element or special wiring is currently required for various voltage applications. It would be desirable therefore to have a heater element which, in combination with a suitable control circuit, would operate under different voltage conditions automatically without the intervention of the user. Such as system, if properly implemented, would also allow for the use of an inexpensive universal heater element.
In addition, U.S. and foreign standards require different operating frequencies which can adversely affect timing circuits and electronic controls. It would therefore be desirable to provide a control circuit which operates satisfactorily without regard to variations in frequency standards.
Other desirable features for a hair curling appliance include accurate temperature sensing, fast barrel temperature recovery when hair is wound on the barrel, indication that the appliance is at a proper operating temperature, automatic shut off, and noise insensitivity in a suitable compact, inexpensive and simple electronics package, with a minimum number of components.